This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application DISPERSIVE OPTICAL FIBER USING BINARY COMPONENT SILICA filed with the Korean Industrial Property Office on Jun. 23, 1998 and there duly assigned Serial No. 23685/1998.
1. Field of the Invention
The present invention relates to a dispersive optical fiber having variable core-cladding refractive index differences depending on wavelength, and more particularly, to a dispersive optical fiber using binary-component silica glass.
2. Description of the Related Art
In general, the refractive index of a material is a function of the wavelength of light. For glasses used in optical fibers, the shorter the wavelength, the higher the refractive index. In conventional optical fibers used in optical devices, the core glass and cladding glass have similar spectral characteristics so that the refractive index difference between them is almost constant with respect to wavelength. The difference between the refractive indices of GeO2 doped silica, used for the core, and SiO2 used for the cladding, is almost constant with respect to wavelength. Therefore, it is not easy to obtain optical fiber devices with various spectral properties by using typical fibers.
An optical fiber having variable refractive index difference between core and cladding depending on wavelength is called a dispersive optical fiber. Optical devices using a dispersive optical fiber include optical fiber filters, wavelength insensitive couplers, wavelength-selective optical fiber couplers and the like.
A dispersive optical fiber has the following properties. First, the refractive index difference between the core and the cladding is dependent upon wavelength. Second, the refractive indices of to the core material and the cladding material become equal at a specific wavelength. Third, according to the wavelength of incident light, the incident light is propagated through either the core or the cladding. Currently known glass materials having highly dispersive characteristics and filter types using the same are shown in the following Table 1.
Conventional dispersive optical fibers are typically composed of multi-component glass and have a transmission loss greater than that of pure silica optical fibers. Also, since they have a low melting point, it is not possible to fusion-splice them with typical optical fibers. The conventional dispersive optical fibers are fabricated using a rod-in-tube technology in which a rod, i.e., a core material, is inserted into a tube, i.e., a cladding material, and heated and softened to remove the gap therebetween, thereby completing the optical fibers. However, the rod-in-tube technology is very complicated. Also, since the refractive index of multi-component glass is higher than that of typical glass, the splicing loss increases due to mechanical splicing of the multi-component glass with the typical glass.
It is therefore an object of the present invention to provide improved long and short wavelength pass, bandpass and band-rejection filters.
It is also an object of the present invention to provide an improved dispersive optical fiber.
It is a further object of the invention to provide a dispersive optical fiber having low transmission loss.
It is a yet further object of the invention to provide a dispersive optical fiber with reduced splicing loss.
It is a still further object of the invention to provide a dispersive optical fiber which may be fusion-spliced.
It is a still yet further object of the invention to provide a dispersive optical fiber which may be fabricated without using rod-in-tube technology.
To achieve the above objectives, the present invention provides a dispersive optical fiber having variable refractive index differences between the core and the cladding depending on wavelength, by using a binary-component silica material, rather than multi-component glass.
Accordingly, there is provided a dispersive optical fiber including a core made of silica doped with a first dispersive material, and a cladding made of silica doped with a second dispersive material, wherein the refractive indices of the first and the second dispersive materials cross each other at a predetermined cross wavelength.